PicoScope 7 Automotive
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Relative compression test
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ademiltonxavier
- Newbie
- Posts: 8
- Joined: Tue Feb 28, 2023 2:32 pm
Relative compression test
Good morning.
I would like someone to know and be able to help me with the relative compression test on agricultural machines, this machine that I am going to make has two 100 amp batteries connected to 12 volts, positive with positive and negative with negative, but its departure is in 24 volts it has an inverter so that the starter motor operates at 24 volts, all the rest of the equipment operates at 12 volts, alternator etc everything, only the starter is at 24 volts, when doing the relative compression test on this equipment I must measure at which battery poles? and how to set it up correctly for the test.
I would like someone to know and be able to help me with the relative compression test on agricultural machines, this machine that I am going to make has two 100 amp batteries connected to 12 volts, positive with positive and negative with negative, but its departure is in 24 volts it has an inverter so that the starter motor operates at 24 volts, all the rest of the equipment operates at 12 volts, alternator etc everything, only the starter is at 24 volts, when doing the relative compression test on this equipment I must measure at which battery poles? and how to set it up correctly for the test.
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ben.martins
- Pico Staff Member
- Posts: 543
- Joined: Tue May 16, 2017 1:02 pm
Re: Relative compression test
Hello,
Thank you for your post and sorry for the late reply. This type of setup is found in a number of places and was even seen on a Toyota Landcruiser at one point!
I have seen this setup on a combine where, as shown in your attachments, the dual batteries are connected in parallel but the starter circuit switches to put them in series and supply 24V to the starter motor.
When it comes to a relative compression test we are looking at either the voltage drop or the current draw during cranking. If you are looking to carry out the test in PicoDiagnostics then I would suggest measuring across just one battery. We're not interested in the overall voltage just the effects on during cranking.
If you're in PicoScope software then a current clamp might be easier. I would suggest getting to the starter motor cable if that is accessible as this will give you the work being done by the starter motor regardless of what the voltage is. If you can't get to the starter motor cable then stick with the batteries but use the front battery. Current is still flowing after all regardless of how the batteries have been arranged by the machine but at least this way you will ensure you see something.
Hope this helps and if you get a chance to post the results, I'd be interested to see how they come out.
Kind regards
Ben
Thank you for your post and sorry for the late reply. This type of setup is found in a number of places and was even seen on a Toyota Landcruiser at one point!
I have seen this setup on a combine where, as shown in your attachments, the dual batteries are connected in parallel but the starter circuit switches to put them in series and supply 24V to the starter motor.
When it comes to a relative compression test we are looking at either the voltage drop or the current draw during cranking. If you are looking to carry out the test in PicoDiagnostics then I would suggest measuring across just one battery. We're not interested in the overall voltage just the effects on during cranking.
If you're in PicoScope software then a current clamp might be easier. I would suggest getting to the starter motor cable if that is accessible as this will give you the work being done by the starter motor regardless of what the voltage is. If you can't get to the starter motor cable then stick with the batteries but use the front battery. Current is still flowing after all regardless of how the batteries have been arranged by the machine but at least this way you will ensure you see something.
Hope this helps and if you get a chance to post the results, I'd be interested to see how they come out.
Kind regards
Ben
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ademiltonxavier
- Newbie
- Posts: 8
- Joined: Tue Feb 28, 2023 2:32 pm
Re: Relative compression test
I did the relative compression measurement on both batteries, I didn't get good results because the cables and terminals were very bad, then I did the current consumption test with the pliers directly on the cable that goes to the starter motor, the access to it It's very easy, I attach the results.
it's a problem the terminals and cables of the machines are all of that kind of bad care.
it's a problem the terminals and cables of the machines are all of that kind of bad care.
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- 20230425-0005-POSITIVO.psdata
- (770.49 KiB) Downloaded 208 times
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- 20230425-0005-NEGATIVO.psdata
- (754.71 KiB) Downloaded 195 times
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- 230425_CompressionTest_002.pddata
- (39.7 KiB) Downloaded 203 times
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- 230425_CompressionTest_001.pddata
- (39.21 KiB) Downloaded 195 times
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